Can you please confirm the version you are running? Are you running PS version 15.2.1 or 14.2.1? Extract Assets is only in PS 15.2 or 15.2.1. You can see the version from the properties of the photoshop application file in the Windows Explorer.

Here's the shot. I have only one version installed. The print is tiny but it is 14.2.1. Like I say it was updated yesterday by clicking on the update button in Creative Cloud. And under the help menu when I check for updates I get a message saying my PS is up to date.